The invention relates to a method for electrohydraulically controlling a motor vehicle transmission and to an electrohydraulic controller for a motor vehicle transmission.
In automatic or automated transmissions for motor vehicles, as well as conventional purely hydraulic controllers combined electronic-hydraulic systemsxe2x80x94referred to below as electrohydraulic controllersxe2x80x94are also being increasingly used. In such systems, the hydraulics continue to actuate the power of the transmission actuatorsxe2x80x94clutches and brakesxe2x80x94while the selection of the gears and transmission ratios and the adaptation of the pressures to the torque to be transmitted is performed by the electronics. The interface between the electronics and hydraulics is usually formed by electrohydraulic transducers, such as electrically actuated proportional pressure regulating valves or servo valves, which convert an impressed control current into an activation pressure, proportional thereto, for an assigned transmission actuator. In order to set with sufficient precision the activation pressure that is necessary for a requested torque, it is necessary to feed back the pressure originating from the electrically actuated pressure regulating valve or the control current that is impressed into the electrically actuated pressure valve. In this way, a closed control circuit is implemented. In this context, stringent requirements are made of the resolution of the fed-back activation pressure or control current, in particular in the low pressure or torque ranges.
When the control current of the electrically actuated pressure regulating valve is fed back, it is possible to make a measurement of the current during which the results lie in a narrow tolerance range which permits the requested resolutions and degrees of precision only by using complex and high-quality, but also expensive, electronics. The activation pressure of the pressure regulating valve can reliably be fed back with the requested precision only by using high-quality and thus expensive pressure sensors in conjunction with correspondingly complex evaluation electronics.
A further possible way of achieving the necessary resolution is to use electronically actuated pressure regulating valves in what is referred to as a xe2x80x9cdual gainxe2x80x9d configuration. Such xe2x80x9cdual gainxe2x80x9d pressure regulating valves have two electro-mechanical transducers per valve, and the necessary resolution can be achieved by two or more regulated driver stages. However, such a solution is also associated with high costs.
It is accordingly an object of the invention to provide a method for electrohydraulically controlling a motor vehicle transmission and a electrohydraulic controller for a motor vehicle transmission which overcome the above-mentioned disadvantages of the prior art methods and devices of this general type, in which the activation pressure of the transmission actuators, and thus of the torques to be set, can be reliably regulated in a precise way with a low level of complexity and at low cost.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for electrohydraulically controlling a motor vehicle transmission. The method includes the steps of using a pressure regulating valve to convert a control current into an activation pressure for a transmission actuator, feeding back the control current and the activation pressure at a given time to a regulator, and using the regulator to convert a setpoint value for the activation pressure of the transmission actuator into the control current. The conversion is dependent on the control current at the given time and/or the activation pressure at the given time.
The pressure regulating valve converts the control current into the activation pressure for a transmission actuator, for example a clutch or a brake. According to the invention, both the control current at a given time is fed back to the regulator via the current measuring device and the activation pressure at the given time is fed back the a regulator via a pressure sensor. The regulator converts a setpoint value for the activation pressure of the transmission actuator, which characterizes a torque to be transmitted by the actuatorxe2x80x94referred to below as an actuator torquexe2x80x94into the control current as a function of the fed-back control current and/or of the fed-back activation pressure. In one advantageous embodiment, the current measuring device is adjusted here in such a way that a high resolution of the measurement results is obtained in a partial range of the actuator torque. In the partial range, the setpoint value for the activation pressure is converted into the control current for the pressure regulating valve in dependence on the fed-back control current. However, given linear adjustment of the current measuring device, reasonable measurement results are no longer supplied outside the partial range. It is therefore decisive to switch over in good time, before the partial range limits are reached, to a conversion of the setpoint pressure that is dependent on the fed-back activation pressure. For this purpose, the regulator advantageously evaluates a variable which characterizes the actuator torque to be transmitted, and when there is upward or downward transgression of predefined threshold values the system is switched over from conversion of the setpoint pressure as a function of control current to the conversion as a function of the activation pressure. The implementation possibilities for the necessary threshold value comparison are very numerous here. For example, the fed-back control current and the fed-back activation pressure can serve as reference variables.
It is particularly advantageous here that the controller according to the invention merely requires a conventional current measuring device and a conventional pressure sensor. In both components, no particular requirements are made of the resolution over a wide measuring range so that cost-effective standard systems can be used. The pressure sensor used can advantageously also be utilized for monitoring purposes.
With the foregoing and other objects in view there is additionally provided, in accordance with the invention, an electrohydraulic controller for a motor vehicle transmission The electrohydraulic controller contains a pressure regulating valve for converting a control current into an activation pressure for a transmission actuator, and a regulator for converting a setpoint value for the activation pressure into the control current in dependence on the control current at a given time and/or the activation pressure at the given time. A current measuring device is connected between the regulator and the pressure regulating valve. The current measuring device feeds back the control current at the given time to the regulator. A pressure sensor is connected between the regulator and the pressure regulating valve, the pressure sensor feeds back the activation pressure at the given time to the regulator.
In accordance with an added feature of the invention, the current measuring device is adjusted such that a high resolution of a measurement result is ensured in a partial range of an actuator torque to be transmitted.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for electrohydraulically controlling a motor vehicle transmission and a electrohydraulic controller for a motor vehicle transmission, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.